/*
 * File      : pthread_rwlock.c
 * This file is part of RT-Thread RTOS
 * COPYRIGHT (C) 2006 - 2010, RT-Thread Development Team
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, write to the Free Software Foundation, Inc.,
 *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Change Logs:
 * Date           Author       Notes
 * 2010-10-26     Bernard      the first version
 */

#include <pthread.h>

int pthread_rwlockattr_init(pthread_rwlockattr_t* attr)
{
	if(!attr)
		return EINVAL;

	*attr = PTHREAD_PROCESS_PRIVATE;

	return 0;
}
RTM_EXPORT(pthread_rwlockattr_init);

int pthread_rwlockattr_destroy(pthread_rwlockattr_t* attr)
{
	if(!attr)
		return EINVAL;

	return 0;
}
RTM_EXPORT(pthread_rwlockattr_destroy);

int pthread_rwlockattr_getpshared(const pthread_rwlockattr_t* attr,
                                  int*                        pshared)
{
	if(!attr || !pshared)
		return EINVAL;

	*pshared = PTHREAD_PROCESS_PRIVATE;

	return 0;
}
RTM_EXPORT(pthread_rwlockattr_getpshared);

int pthread_rwlockattr_setpshared(pthread_rwlockattr_t* attr, int pshared)
{
	if(!attr || pshared != PTHREAD_PROCESS_PRIVATE)
		return EINVAL;

	return 0;
}
RTM_EXPORT(pthread_rwlockattr_setpshared);

int pthread_rwlock_init(pthread_rwlock_t*           rwlock,
                        const pthread_rwlockattr_t* attr)
{
	if(!rwlock)
		return EINVAL;

	rwlock->attr = PTHREAD_PROCESS_PRIVATE;
	pthread_mutex_init(&(rwlock->rw_mutex), NULL);
	pthread_cond_init(&(rwlock->rw_condreaders), NULL);
	pthread_cond_init(&(rwlock->rw_condwriters), NULL);

	rwlock->rw_nwaitwriters = 0;
	rwlock->rw_nwaitreaders = 0;
	rwlock->rw_refcount = 0;

	return 0;
}
RTM_EXPORT(pthread_rwlock_init);

int pthread_rwlock_destroy(pthread_rwlock_t* rwlock)
{
	int result;

	if(!rwlock)
		return EINVAL;

	if(rwlock->attr == -1)
		return 0; /* rwlock is not initialized */

	if((result = pthread_mutex_lock(&rwlock->rw_mutex)) != 0)
		return(result);

	if(rwlock->rw_refcount != 0 ||
	        rwlock->rw_nwaitreaders != 0 ||
	        rwlock->rw_nwaitwriters != 0) {
		result = EBUSY;

		return result;
	} else {
		/* check whether busy */
		result = rt_sem_trytake(&(rwlock->rw_condreaders.sem));

		if(result == RT_EOK) {
			result = rt_sem_trytake(&(rwlock->rw_condwriters.sem));

			if(result == RT_EOK) {
				rt_sem_release(&(rwlock->rw_condreaders.sem));
				rt_sem_release(&(rwlock->rw_condwriters.sem));

				pthread_cond_destroy(&rwlock->rw_condreaders);
				pthread_cond_destroy(&rwlock->rw_condwriters);
			} else {
				rt_sem_release(&(rwlock->rw_condreaders.sem));
				result = EBUSY;
			}
		} else
			result = EBUSY;
	}

	pthread_mutex_unlock(&rwlock->rw_mutex);

	if(result == 0)
		pthread_mutex_destroy(&rwlock->rw_mutex);

	return result;
}
RTM_EXPORT(pthread_rwlock_destroy);

int pthread_rwlock_rdlock(pthread_rwlock_t* rwlock)
{
	int result;

	if(!rwlock)
		return EINVAL;

	if(rwlock->attr == -1)
		pthread_rwlock_init(rwlock, NULL);

	if((result = pthread_mutex_lock(&rwlock->rw_mutex)) != 0)
		return(result);

	/* give preference to waiting writers */
	while(rwlock->rw_refcount < 0 || rwlock->rw_nwaitwriters > 0) {
		rwlock->rw_nwaitreaders++;
		/* rw_mutex will be released when waiting for rw_condreaders */
		result = pthread_cond_wait(&rwlock->rw_condreaders, &rwlock->rw_mutex);
		/* rw_mutex should have been taken again when returned from waiting */
		rwlock->rw_nwaitreaders--;

		if(result != 0)  /* wait error */
			break;
	}

	/* another reader has a read lock */
	if(result == 0)
		rwlock->rw_refcount++;

	pthread_mutex_unlock(&rwlock->rw_mutex);

	return (result);
}
RTM_EXPORT(pthread_rwlock_rdlock);

int pthread_rwlock_tryrdlock(pthread_rwlock_t* rwlock)
{
	int result;

	if(!rwlock)
		return EINVAL;

	if(rwlock->attr == -1)
		pthread_rwlock_init(rwlock, NULL);

	if((result = pthread_mutex_lock(&rwlock->rw_mutex)) != 0)
		return(result);

	if(rwlock->rw_refcount < 0 || rwlock->rw_nwaitwriters > 0)
		result = EBUSY;                 /* held by a writer or waiting writers */
	else
		rwlock->rw_refcount++;          /* increment count of reader locks */

	pthread_mutex_unlock(&rwlock->rw_mutex);

	return(result);
}
RTM_EXPORT(pthread_rwlock_tryrdlock);

int pthread_rwlock_timedrdlock(pthread_rwlock_t*      rwlock,
                               const struct timespec* abstime)
{
	int result;

	if(!rwlock)
		return EINVAL;

	if(rwlock->attr == -1)
		pthread_rwlock_init(rwlock, NULL);

	if((result = pthread_mutex_lock(&rwlock->rw_mutex)) != 0)
		return(result);

	/* give preference to waiting writers */
	while(rwlock->rw_refcount < 0 || rwlock->rw_nwaitwriters > 0) {
		rwlock->rw_nwaitreaders++;
		/* rw_mutex will be released when waiting for rw_condreaders */
		result = pthread_cond_timedwait(&rwlock->rw_condreaders, &rwlock->rw_mutex, abstime);
		/* rw_mutex should have been taken again when returned from waiting */
		rwlock->rw_nwaitreaders--;

		if(result != 0)
			break;
	}

	/* another reader has a read lock */
	if(result == 0)
		rwlock->rw_refcount++;

	pthread_mutex_unlock(&rwlock->rw_mutex);

	return (result);
}
RTM_EXPORT(pthread_rwlock_timedrdlock);

int pthread_rwlock_timedwrlock(pthread_rwlock_t*      rwlock,
                               const struct timespec* abstime)
{
	int result;

	if(!rwlock)
		return EINVAL;

	if(rwlock->attr == -1)
		pthread_rwlock_init(rwlock, NULL);

	if((result = pthread_mutex_lock(&rwlock->rw_mutex)) != 0)
		return(result);

	while(rwlock->rw_refcount != 0) {
		rwlock->rw_nwaitwriters++;
		/* rw_mutex will be released when waiting for rw_condwriters */
		result = pthread_cond_timedwait(&rwlock->rw_condwriters, &rwlock->rw_mutex, abstime);
		/* rw_mutex should have been taken again when returned from waiting */
		rwlock->rw_nwaitwriters--;

		if(result != 0)
			break;
	}

	if(result == 0)
		rwlock->rw_refcount = -1;

	pthread_mutex_unlock(&rwlock->rw_mutex);

	return(result);
}
RTM_EXPORT(pthread_rwlock_timedwrlock);

int pthread_rwlock_trywrlock(pthread_rwlock_t* rwlock)
{
	int result;

	if(!rwlock)
		return EINVAL;

	if(rwlock->attr == -1)
		pthread_rwlock_init(rwlock, NULL);

	if((result = pthread_mutex_lock(&rwlock->rw_mutex)) != 0)
		return(result);

	if(rwlock->rw_refcount != 0)
		result = EBUSY;                 /* held by either writer or reader(s) */
	else
		rwlock->rw_refcount = -1;       /* available, indicate a writer has it */

	pthread_mutex_unlock(&rwlock->rw_mutex);

	return(result);
}
RTM_EXPORT(pthread_rwlock_trywrlock);

int pthread_rwlock_unlock(pthread_rwlock_t* rwlock)
{
	int result;

	if(!rwlock)
		return EINVAL;

	if(rwlock->attr == -1)
		pthread_rwlock_init(rwlock, NULL);

	if((result = pthread_mutex_lock(&rwlock->rw_mutex)) != 0)
		return(result);

	if(rwlock->rw_refcount > 0)
		rwlock->rw_refcount--;              /* releasing a reader */
	else if(rwlock->rw_refcount == -1)
		rwlock->rw_refcount = 0;            /* releasing a writer */

	/* give preference to waiting writers over waiting readers */
	if(rwlock->rw_nwaitwriters > 0) {
		if(rwlock->rw_refcount == 0)
			result = pthread_cond_signal(&rwlock->rw_condwriters);
	} else if(rwlock->rw_nwaitreaders > 0) {
		result = pthread_cond_broadcast(&rwlock->rw_condreaders);
	}

	pthread_mutex_unlock(&rwlock->rw_mutex);

	return(result);
}
RTM_EXPORT(pthread_rwlock_unlock);

int pthread_rwlock_wrlock(pthread_rwlock_t* rwlock)
{
	int result;

	if(!rwlock)
		return EINVAL;

	if(rwlock->attr == -1)
		pthread_rwlock_init(rwlock, NULL);

	if((result = pthread_mutex_lock(&rwlock->rw_mutex)) != 0)
		return(result);

	while(rwlock->rw_refcount != 0) {
		rwlock->rw_nwaitwriters++;
		/* rw_mutex will be released when waiting for rw_condwriters */
		result = pthread_cond_wait(&rwlock->rw_condwriters, &rwlock->rw_mutex);
		/* rw_mutex should have been taken again when returned from waiting */
		rwlock->rw_nwaitwriters--;

		if(result != 0)
			break;
	}

	if(result == 0)
		rwlock->rw_refcount = -1;

	pthread_mutex_unlock(&rwlock->rw_mutex);

	return(result);
}
RTM_EXPORT(pthread_rwlock_wrlock);

